Effects of air pollutants on the wintertime water economy of the Scots pine Pinus silvestris

The changes effected by air-borne pollutants in the wintertime water economy of the Scots pine were investigated in industrial and urban environments in Oulu (65°N). Pine needles were found to undergo a wintertime water stress, which was more intense in the polluted area than in the less polluted environment. The water stress of the needles was found to be the more severe, the more pollutants had accumulated in the needles. In the needles of the trees growing in the polluted area, transpiration started shortly after they had been brought into laboratory even at midwinter, but the healthy trees were not equally sensitive in their response. When the weight loss of branches was observed in outdoor conditions, it was noted that the branches brought from the polluted area lost weight more rapidly than the branches of the healthy area. Air-borne pollutants hence constitute an obvious additional risk to the wintering of plants, particularly their water economy.